This invention relates to an epoxidation process comprising reacting an olefin, hydrogen and oxygen in a liquid medium in the presence of a solid epoxidation catalyst in a reactor system that facilitates transfer of the hydrogen and oxygen to the liquid and the solid epoxidation catalyst.
Many different methods for the preparation of epoxides have been developed. Generally, epoxides are formed by the reaction of an olefin with an oxidizing agent in the presence of a catalyst. The production of propylene oxide from propylene and an organic hydroperoxide oxidizing agent, such as ethyl benzene hydroperoxide or tert-butyl hydroperoxide, is commercially practiced technology. This process is performed in the presence of a solubilized molybdenum catalyst, see U.S. Pat. No. 3,351,635, or a heterogeneous titania on silica catalyst, see U.S. Pat. No. 4,367,342. Hydrogen peroxide is another oxidizing agent useful for the preparation of epoxides. Olefin epoxidation using hydrogen peroxide and a titanium silicate zeolite is demonstrated in U.S. Pat. No. 4,833,260. One disadvantage of both of these processes is the need to pre-form the oxidizing agent prior to reaction with olefin.
Another commercially practiced technology is the direct epoxidation of ethylene to ethylene oxide by reaction with oxygen over a silver catalyst. Unfortunately, the silver catalyst has not proved very useful in epoxidation of higher olefins. Therefore, much current research has focused on the direct epoxidation of higher olefins with oxygen and hydrogen in the presence of a different catalyst system. In this process, it is believed that oxygen and hydrogen react in situ to form an oxidizing agent. Thus, development of an efficient process (and catalyst) promises less expensive technology compared to the commercial technologies that employ pre-formed oxidizing agents.
Many different catalysts have been proposed for use in the direct epoxidation of higher olefins. For example, JP 4-352771 discloses the epoxidation of propylene oxide from the reaction of propylene, oxygen, and hydrogen using a catalyst containing a Group VIII metal such as palladium on a crystalline titanosilicate. U.S. Pat. No. 5,859,265 discloses a catalyst in which a platinum metal, selected from Ru, Rh, Pd, Os, Ir and Pt, is supported on a titanium or vanadium silicalite. Other examples include gold supported on titanium oxide, see for example U.S. Pat. No. 5,623,090, and gold supported on titanosilicates, see for example PCT Intl. Appl. WO 98/00413.
Because the direct epoxidation of olefins requires the mass transfer of gases into a liquid in order to achieve maximum rate and selectivity, reactor designs that would facilitate this mass transfer are needed. Thus, favorable reactor designs are necessary to allow increased rates and selectivity in the process. U.S. Pat. No. 5,972,661 describes a mixing system for the circulation and gas-liquid contacting of liquids in a tank that is especially useful for bio-reaction process such as fermentation. However, U.S. Pat. No. 5,972,661 does not describe the use of the reactor system with solid catalysts to facilitate gas-liquid-solid mass transfer.
In sum, new direct epoxidation processes are required to allow for efficient gas-liquid-solid contact to achieve maximum rate and selectivity to epoxide. In particular, increasing the selectivity to epoxide, the productivity of the catalyst, and extending the useful life of the catalyst would significantly enhance the commercial potential of direct epoxidation.
The invention is an olefin epoxidation process that comprises reacting olefin, oxygen, and hydrogen in a liquid medium in the presence of an epoxidation catalyst in a reactor system for circulating a liquid medium in a tank that facilitates transfer of the hydrogen and oxygen to the liquid medium. The reactor system provides a high degree of liquid circulation and micro-mixing of a multiphase liquid medium, enabling the desired simultaneous contacting and mass transfer between the liquid phase in the tank with a gas and a solid epoxidation catalyst.